Flux-free Joining of Aluminium Composite Materials

Abstract

Use of an aluminium composite material in a thermal joining method, said material consisting of at least one aluminium core alloy and at least one external brazing layer consisting of an aluminium brazing alloy provided on one or both sides of the aluminium core alloy, wherein the aluminium brazing layer has a pickled surface. Reduced costs and a lower environmental impact is achieved by using an aluminium composite material in which the pickled surface of the aluminium brazing layer had been pickled by pickling with an acid, aqueous pickling solution containing at least one mineral acid and at least one complex-forming agent or a complexing mineral acid, wherein the removal of material in the pickling is between 0.05 g/m² and 6 g/m², the aluminium composite material is used in a flux-free, thermal joining method, and the joining method is carried out in the presence of a protective gas.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS[0001]This patent application is a continuation of PCT / EP2014 / 077519, filed Dec. 12, 2014, which claims priority to European Application No. 13197108.7, filed Dec. 13, 2013, the entire teachings and disclosure of which are incorporated herein by reference thereto.FIELD OF THE INVENTION[0002]The invention relates to the use of an aluminium composite material consisting of at least one aluminium core alloy and at least one external brazing layer consisting of an aluminium brazing alloy provided on one or on both sides of the aluminium core alloy, wherein the aluminium brazing layer has a pickled surface and wherein the aluminium composite material is used in a flux-free, thermal joining method and the joining method is carried out in the presence of a protective gas. The invention also relates to a method for producing a strip-shaped aluminium composite material consisting of at least one aluminium core alloy and at least one external braz...

AI Technical Summary

Benefits of technology

[0052]The treatment time can be reduced further if the temperature of the pickling solution is 40° C. to 85° C., since in this way the reactivity of the reagents is further increased. Temperatures above 85° C. require additional measures with no significant gain in processing speed. A preferred temperature range is therefore 50° C. to 60° C.

[0053]According to a third teaching of the present invention the object is achieved by a method for the thermal joining of structural parts of an aluminium alloy in the use according to the invention of an aluminium composite material, in which the aluminium composite material comprises at least one aluminium core alloy and at least one external brazing layer consisting of an aluminium brazing alloy provided on one or on both sides of the aluminium core alloy, wherein the aluminium brazing layer has a surface pickled with a method according to the invention, the aluminium composite material is joined in a flux-free, thermal joining method, and the joining method takes place in the presence of a protective gas. Owing to the use of a protective gas, for example nitrogen, the formation of an oxide film on the surface of the liquid brazing material is prevented, which has a significantly higher melting point and as a result the brazing process is hindered. It has been found that in the thermal joining using a protective gas in the use according to the invention of the aluminium composite materials with an acid pickled surface, in which the surface was pickled with a mixture of a mineral acid and a complex-forming agent or a complexing mineral acid, high quality brazing results are achieved also without the use of fluxes. This was not possible up to now, especially with a single-layer structure of the aluminium brazing layer.

[0054]Particularly advantageous therefore are also the thermally joined constructions produced by the method, comprising at least a first and a second thermally joined part, wherein at least one of the parts comprises an aluminium composit

Problems solved by technology

If the removal of material is for example less than 0.05 g/m2, only poor brazing results are achieved.

A removal of material gr

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